Android LruCache & DiskLruCache cooperate working in ListView

package zhangphil.cache;

import android.app.ListActivity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.os.Bundle;
import android.util.Log;
import android.util.LruCache;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;

import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.MessageDigest;

public class MainActivity extends ListActivity {
    private LruCache mLruCache;
    private DiskLruCache mDiskLruCache;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        int CACHE_SIZE = 8 * 1024 * 1024;
        mLruCache = new LruCache(CACHE_SIZE);
        try {
            mDiskLruCache = DiskLruCache.open(this.getCacheDir(), 1, 1, CACHE_SIZE * 10);
        } catch (Exception e) {
            e.printStackTrace();
        }

        ArrayAdapter mAdapter = new ArrayAdapter(this, 0) {
            @NonNull
            @Override
            public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
                ImageView image = new ImageView(getContext());
                load(R.mipmap.ic_launcher, image);
                return image;
            }

            @Override
            public int getCount() {
                return 20;
            }
        };

        setListAdapter(mAdapter);
    }

    private void load(int id, ImageView image) {
        String key = null;

        if (id == R.mipmap.ic_launcher) {
            key = getMD5("R.mipmap.ic_launcher");
        }

        //首先查找LruCache中的缓存
        Bitmap bmp = mLruCache.get(key);
        if (bmp == null) {
            Log.d("LruCache缓存", "没有，继续深入到DiskLruCache读取。");

            bmp = readFromDiskLruCache(key);

            if (bmp == null) {
                Log.d("LruCache与DiskLruCache", "没有缓存，开始创建新数据资源并缓存之。");
                bmp = BitmapFactory.decodeResource(getResources(), id);

                //初次创建新资源，更新到DiskLruCache
                writeToDiskLruCache(key, bmp);
            } else {
                image.setImageBitmap(bmp);
            }

            //更新到LruCache缓存中，以待下一次使用。
            mLruCache.put(key, bmp);
            Log.d("LruCache缓存", "写入完成。");
        } else {
            //命中缓存
            Log.d("LruCache缓存", "已有，复用。");
            image.setImageBitmap(bmp);
        }
    }

    private void writeToDiskLruCache(String key, Bitmap bmp) {
        try {
            DiskLruCache.Editor editor = mDiskLruCache.edit(key);

            //把Bitmap转化为byte数组存储
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            bmp.compress(Bitmap.CompressFormat.PNG, 100, baos);
            byte[] bytes = baos.toByteArray();

            //再次把Bitmap数组写进为DiskLruCache准备的输出流。
            OutputStream os = editor.newOutputStream(0);
            os.write(bytes);
            os.flush();

            //正式写入DiskLruCache
            editor.commit();

            Log.d("DiskLruCache缓存", "写入缓存资源完毕。");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private Bitmap readFromDiskLruCache(String key) {
        DiskLruCache.Snapshot snapShot = null;
        try {
            snapShot = mDiskLruCache.get(key);
        } catch (Exception e) {
            e.printStackTrace();
        }

        Bitmap bmp = null;
        if (snapShot != null) {
            Log.d("DiskLruCache缓存", "发现资源，复用。");
            InputStream is = snapShot.getInputStream(0);
            bmp = BitmapFactory.decodeStream(is);
        } else {
            Log.d("DiskLruCache缓存", "没有发现缓存资源。");
        }

        return bmp;
    }

    private String getMD5(String msg) {
        MessageDigest md = null;

        try {
            md = MessageDigest.getInstance("MD5");
        } catch (Exception e) {
            e.printStackTrace();
        }

        md.reset();
        md.update(msg.getBytes());

        byte[] bytes = md.digest();

        String result = "";
        for (byte b : bytes) {
            result += String.format("%02x", b);
        }

        return result;
    }
}